Photochemical production of naphthenic hydrocarbons



.l' atented pr. 28, 153

PHOTO CHEMICAL PRODUCTION OF NAPHTHENIC HYDRUCARBONS Delaware No Drawing. Application December 29, 1949, Serial No. 135,842

3 Glaims.

l The present invention is directed to the production of cyclic hydrocarbons from non-cyclic hydrocarbons. More particularly, the present invention is directed to cyclization of certain parafiinic hydrocarbons to form naphthenes.

The main object of the present invention is to produce naphthenes from parafilnic hydrocarbons by cyclization of the latter. A still further object of the present invention is to provide a process wherein paraifinic hydrocarbons are caused to undergo cyclization through the agency of radiant energy.

The present invention may be briefly described as a process wherein naphthenic hydrocarbons are produced from certain parafiinic hydrocaroons by subjecting the latter in admixture with a metallic sensitizer to radiant energy of a wave length at which the sensitizer absorbs and becomes activated, at a temperature in the range of 80 F. to 650 F. On completion of the reaction period, the unconverted paraifinic hydrocarbons and the metal sensitizer may be sepafrom the naphthenic product recycled to the reactor for further conversion.

The parafiinic hydrocarbons which may be embeing attached to a carbon atom which is in the 5, 6, '7, or 8 position; and (3) those dialkyl substituted parafiinic hydrocarbons having at least six carbon atoms and not more than nine carbon atoms in a straight chain and having no more than 11 carbon atoms in the molecule, the

alkyl substituent groups containing not more than two carbon atoms each, one alkyl substituent group being attached to a carbon atom which is in the 5, 6, 7, or 8 position and the other alkyl aubstituent group being attached to any other carbon atom in the chain, but preferably to a carbon atom separated by three or four carbon atoms from that to which the other alkyl subitituent group is attached. In other words, the hydrocarbons which are amenable to conversion according to the present invention are those parafilnic hydrocarbons having from six to nine carbon atoms in a straight chain in a molecule of no more than 11 carbon atoms, none of which.

are quaternary, and having from 0 to 2 alkyl substituent groups of no more than two carbon atoms each, one of said groups being attached to a carbon atom of the straight chain selected from the fifth, sixth, seventh, and eighth. The normal parafilnic hydrocarbons n-hexane, n-heptane, noctane, and n-nonane come within this category. Among the mono-allryl substituted paramns in this category, the following may be mentioned: isoheptane, Z-methyl heptane, 3-ethy1 heptane, E-methyl octane, 3-methyl octane, S-ethyl octane, l-methyl octane, l-ethyl octane, Z-methyl nonane, 3-ethyl nonane, ii-methyl nonane, and 5- ethyl nonane. The following are among the preferred diallryl substituted parafiins within this category: 2,6-dimethyl heptane; 2,6-dimethyl octane; 2,7-dimethyl octane; 2,6-dimethyl nonane; 3,7-dimethyl nonane; and 2-methyl, S-ethyl octane. Among other dialkyl substituted parafins within this category are the following: 2,5-dimethyl hexane; 2-methyl, 5-ethyl heptane; 2,7- dimethyl octane; 2 methyl, 4-ethyl octane; and others. It will be understood, of course, that although the aforementioned hydrocarbons may each be employed in their pure form it is within the scope of the present invention to employ admixtures of these hydrocarbons or to employ a hydrocarbon feed stock containing other compounds in addition to those aforementioned. It should be mentioned, however, that the feed stock should not contain impurities which destroy the activational capabilities of the metallic sensitizer used in the reaction.

The metal sensitizer may be any metal which meets the conditions set out below, including proper vapor pressure, absorption characteristics, and energy content in the activated state. Whatever metal sensitizer is employed, the vapors thereof are admixed with the paraffinic hydrocarbon feed and the resulting admixture subjected to radiant energy containing frequencies which are capable of energizing the metallic sensitizer. In selecting a metallic sensitizer and source of radiant energy for the reaction, the following conditions must be met:

(A) vapor pressure or the metal employed as a sensitizer must be sufficient to insure that metal vapor is present in the hydrocarbon mixture in a concentration sufficient to absorb the activating light efficiently and to an extent that will permit rapid reaction to take place; conveniently, this vapor pressure is at least 0.001 mm. of mercury at a temperature below about 650 R;

(B) The radiant energy must be or a frequency that can be absorbed by the metallic sensitiaer in its ground state in the reaction mixture. This frequency must correspond to at least one of h resonance lines of the metal sensitizer;

(C) The sum of the energy oi the resonance frequency absorbed by the metal sensitizer'and of the energy of the metal-hydrogen bond must correspond to an energy content equal to, or in excess of that required to rupture one of the carbon to hydrogen bonds of the paraffinic hydrocarbon molecule. The manner in which the bond energies may be calculated is described in detail in an article entitled Dissociation energies of carbon bonds, and resonance energies in hydrocarbon radicals, by J. S. Roberts and H. A. Skinner in Transactions of the Faraday Societsu vol. XLV, pp. 339-357 (1949).

While a relatively large number of metals meet some of these requirements, the most suitable metal sensitizers for my invention are the metals jacket prior to the beginning of the reaction."

of sub-group B or group II of the periodic table,

namely zinc, cadmium, and mercury. Because of the magnitude of their vapor pressures, mercury and cadmium are preferred. The table below indicates the approximate frequencies at which the aforementioned sensitizers may be activated.

TABLE Resonance Element Lines,

The temperature at which the reaction is conducted is in the range of a minimum of about 80 F. to a maximum of about 650 F. and the most favorable temperature in a particular instance will depend to some extent upon the nature of the hydrocarbons in the feed mixture but largely upon the metallic sensitizer employed. Good yields of naphthenes are secured when operating at temperatures in the lower portion of the range, that is, at temperatures ranging from about 80 F. to about 250 F., when mercury is used as the sensitizer. On the other hand, temperatures in the range of from about 250 F. to about 650 F. are preferably employed when cadmium is used as the. sensitizer, and in the range of 400 F. to 650 F. when zinc is used as the sensitizer, because of the lower vapor pressure of cadmium and zinc as compared to mercury.

Although I prefer to conduct the process of the present invention at about atmospheric pressure, it may with equal facility be carried out at superatmospheric pressures. Pressures as high as 50 atmospheres, or even higher, may be employed.

The process of the present invention is not limited to any particular type of equipment. The

reaction has been carried out satisfactorily in an annular reactor consisting of a cylindrical outer jacket provided with an inlet at one end and an outlet at the other end, the inner cylinder emanating light of the desired wave length. For example, when it is desired to employ mercury as the metallic sensitizer, a mercury vapor lamp emanating light of 2537 A. wave length is inserted as a concentric inner cylinder in the Pyrex jacket. When employing mercury sensitizer, the lamp should be operated in such a manner that an unreversed 2537 A. line is obtained. A satisfactory lamp for such a purpose is, for example, the 15 watt T-8 Germicidal Lamp, or a lamp such 4 as described in U. S. Patent No. 2,473,642, Found et al. When cadmium is used as the metallic sensitizer, a cadmium lamp may be employed. The reactor jacket may be surrounded with a suitable heating means such as an electric heater or a furnace. In converting paraffinic hydrocarbons to naphthenic hydrocarbons in accordance with the present invention, the parafiinic hydrocarbon feed is vaporized and introduced into the jacket through the inlet, and the products of reaction are withdrawn through the outlet. In carrying out a mercury-sensitized reaction, a'satisfactory method of maintaining a mercury sensitlzer in the reactor has been to place a small amount of metallic mercury into the reactor Other satisfactory methods of introducing metal sensitlzer may be employed; for example, a carrier stream. consisting of the vaporized hydrocarbon feed, or a portion thereof, or an inert gas, such as nitrogen, may be passed through a vesse containing the metal sensitizer in the liquid or vapor state, prior to passing said carrier stream into the reaction zone.

In preparing the feed stock for carrying out the process according to my invention, the conventional methods of purification, such as solvent extraction or fractionation, may be employed to obtain a feed stock consisting substantially of a single paraflin hydrocarbon of the character hereinbefore indicated or mixtures thereof. If reactive hydrocarbons other than paraffins are present in the feed, the cyclization according to my invention will still take place but a decreased yield may be expected due to the formation of byproducts from a number of side reactions. Attention shduld also be paid to the exclusion of impurities which may react with the feed or sensitizer to produce undesirable contaminating products. For example, water vapor, in low concentration, may not be harmful to the mercury sensitizer, but it may oxidize cadmium. Reactive compounds, as mentioned above, may cause reactions other than cyclization to take place even though they may not cause the sensltizer to deteriorate.

The. effluent leaving the reactor in which a process according to my invention is carried out may contain unconverted feed hydrocarbon as well as the cyclized product. This total efiluent may be subjected to condensation, to recover the feed and cyclizecl hydrocarbon in the liquid phase and hydrogen and other non-condensables in the gas phase. A part of the total liquid effluent may be recycled to the reactor to increase the yield of cyclized product from the original feed, and a part or all of the total liquid effluent may be subjected to processes such as fractional distillation, or solvent extraction, or extraction with a solid absorbent such as silica gel, in order to 1 recover the cyclized hydrocarbon in substantially pure form. Alternately, the naphthenes may be separated and recovered from the reactor efiluent and the paraifinic hydrocarbons in the eiiiuent recycled'to the reactor.

If the rate offiow through the reactoris such that appreciable quantities of the metal sensitizer are carried out of the reactor in the product stream, then it may be desirable to employ suitable means for recovering the metal sensitizer from the reactor efiluent. This may be in the form of a condenser maintained at. a low temperature, or, in the case where mercury. is the sensitizer metal, it may be abed. of a metal with:

a which mercury may be amalgamated, such, for example, as zinc or copper.

In order to illustrate the invention further. reference is made to the following examples:

Example I Liquid mercury was introduced into the Pyrex jacket of the hereinbefore described apparatus and the jacket heated to a temperature of 250 F. Normal heptane, which had been vaporized and preheated to a temperature of 217 was passed through the Pyrex jacket at a rate of about 1 volume of vapor (measured at C. and 1 atmosphere pressure) per 4 volumes of reactor space per minute. The reaction was continued for two hours and the Pyrex jacket was maintained at a temperature of 250 F. for the duration of this time. The pressure inside the Pyrex jacket was about 760 millimeters of mercury. The product continuously withdrawn from the outlet connection of the Pyrex jacket and recovered by condensation was analyzed by a combination of mass spectrometry and chemical methods and found to consist of 88% normal heptane, 0.1% of olefins, 8.9% of naphthenes, and 3% of paraffins other than normal heptane.

Example II Liquid mercury was introduced into the Pyrex jacket of the hereinbefore described apparatus and the jacket heated to a temperature of 450 F. Normal heptane, which had been vaporized and preheated to a temperature of approximately 450 F., was passed through the Pyrex jacket at a rate of about 1 volume of vapor (measured at 0 C. and 1 atmosphere of pressure) per 4 volumes of reactor space per minute. The reaction was continued for two hours and the Pyrex jacket was maintained at a temperature of 450 F. for the duration of this period. The pressure inside the Pyrex jacket was about 760 millimeters of mercury. The product was continuously withdrawn from the outlet connection of the Pyrex jacket and recovered by condensation. Analysis of the product showed it to consist of 94% normal heptane, 1.4% of olefins, and 4.6% of naphthenes.

Example III Liquid mercury was introduced into the Pyrex jacket of the hereinbefore described apparatus and the jacket heated to a temperature of 550 F. Normal heptane, which had been vaporized and preheated to a temperature of approximately 550 F., was passed through the Pyrex jacket at a rate of about 1 volume of vapor (measured at 0 C. and 1 atmosphere of pressure) per 4 volumes of reactor space per minute. The reaction was continued for two hours and the Pyrex jacket was maintained at a temperature of 550 F. for the duration of this period. The pressure inside the Pyrex jacket was about 760 millimeters of mercury. The product was continuously withdrawn from the outlet connection of the Pyrex jacket and recovered by condensation. Analysi of the product showed it to consist of 96% normal G heptane, 1.4% of olefins, 1.6% of naphthenes, and 1.0% of paraflins other than normal heptane.

From the foregoing examples, it will be seen that parafifinic hydrocarbons of the character hereinbefore described may be converted to naphthenes in good yields by the process of the present invention.

What I wish to claim as new and useful and to secure by Letters Patent is:

1. A method for producing naphthenic hydrocarbons from paraflinic hydrocarbons which comprises the steps of forming a mixture of mercury vapor as a sensitizer and the vapor of a, parafiinic hydrocarbon comprising parafiinic hydrocarbons having from six to nine carbon atoms in a straight chain in a molecule of no more than eleven carbon atoms, none of which are quaternary, and having from zero to two alkyl substituent groups having no more than two carbon atoms each, one of said groups being attached to a carbon atom of said straight chain at least four carbon atoms removed from a terminal carbon atom of the chain, continuously passing the admixture through a reaction zone in a vaporous stream at a rate of one volume of vapor measured at 0 C. and at atmospheric pressure for four volumes of reactor space per minute, and subjecting said mixture in said reaction zone at a temperature in the range of and 650 F. at a pressure at least atmospheric to a resonance energy frequency corresponding at least to one of the resonance lines of said sensitizer and capable of being absorbed by said mixture to form a product comprising naphthenes.

2. A method in accordance with claim 1 in which the paraffinic hydrocarbons are normal paraffins having from 6 to 9 carbon atoms in the molecule.

3. A method in accordance with claim 1 in which the normal parafiin is normal heptane.

HARRY E. CIER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,746,168 Taylor 1 Feb. 4, 1930 2,462,669 Percy Feb. 22, 1949 FOREIGN PATENTS Number Country Date 307,406 Great Britain Mar. 4, 1929 OTHER REFERENCES Olson et al., Journal American Chemical 

1. A METHOD FOR PRODUCING NAPHTHENIC HYDROCARBONS FROM PARAFFINIC HYDROCARBONS WHICH COMPRISES THE STEPS OF FORMING A MIXTURE OF MERCURY VAPOR AS A SENSITIZER AND THE VAPOR OF A PARAFFINIC HYDROCARBON COMPRISING PARAFFINIC HYDROCARBONS HAVING FROM SIX TO NINE CARBON ATOMS IN A STRAIGHT CHAIN IN A MOLECULE OF NO MORE THAN ELEVEN CARBON ATOMS,NONE OF WHICH ARE QUARTERNARY, AND HAVING FROM ZERO TO TWO ALKYL SUBSTITUENT GROUPS HAVING NO MORE THAN TWO CARBON ATOMS EACH, ONE OF SAID GROUPS BEING ATTACHED TO A CARBON ATOM OF SAID STRAIGHT CHAIN AT LEAST FOUR CARBON ATOMS REMOVED FROM A TERMINAL CARBON ATOM OF THE CHAIN, CONTINUOUSLY PASSING THE ADMIXTURE THROUGH A REACTION ZONE IN A VAPOROUS STREAM AT A RATE OF ONE VOLUME OF VAPOR MEASURED AT 0* C. AND AT ATMOSPHERIC PRESSURE FOR FOUR VOLUMES OF REACTOR SPACE PER MINUTE, AND SUBJECTING SAID MIXTURE IN SAID REACTION ZONE AT A TEMPERATURE IN THE RANGE OF 80* AND 650* F. AT A PRESSURE AT LEAST ATMOSPHERIC TO A RESONANCE ENERGY FREQUENCY CORREPONDING AT LEAST TO ONE OF THE RESONANCE LINES OF SAID SENSITIZER AND CAPABLE OF BEING ABSORBED BY SAID MIXTURE TO FORM A PRODUCT COMPRISING NAPHTHENES. 